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Incorrect!

When are exhaust brakes most efficient?

At high engine speed, while in low gears
Correct answer
At low engine speed, while in high gears
During stop/start town work
While travelling at a constant speed on a motorway
You selected this answer

DVSA theory test explanation

An exhaust brake alters the engine's exhaust flow, using it to help control the vehicle's speed. It's most efficient when the engine is running at a high speed and the vehicle is in a low gear, such as when descending a long hill. Using the exhaust brake can relieve the service brakes, preventing them from overheating and fading.

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